DC offset cancelation for wireless communications

ABSTRACT

Techniques are disclosed relating to DC interference cancelation in received wireless signals. Disclosed techniques may be performed in the digital domain, in conjunction with analog cancelation techniques. In some embodiments, a receiver apparatus operates a local oscillator at a frequency corresponding to a particular pilot symbol in a received wireless signal. In some embodiments the receiver estimates DC interference at the frequency based on the received pilot symbol (this may be facilitated by the fact that the contents of pilot symbols are known, because they are typically used for channel estimation). In some embodiments, the receiver apparatus is configured to cancel the DC interference based on the estimate to determine received data in subsequently received signals at the frequency. Disclosed techniques may allow narrowband receivers to efficiently use more of their allocated frequency bandwidth, rather than wasting bandwidth near the frequency of the local oscillator.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.15/375,245, filed Dec. 12, 2016, which claims the benefit of U.S.Provisional Application No. 62/275,286, filed on Jan. 6, 2016. Each ofthe above-referenced applications is incorporated by reference herein inits entirety.

The claims in the instant application are different than those of theparent application or other related applications. The Applicanttherefore rescinds any disclaimer of claim scope made in the parentapplication or any predecessor application in relation to the instantapplication. The Examiner is therefore advised that any such previousdisclaimer and the cited references that it was made to avoid, may needto be revisited. Further, any disclaimer made in the instant applicationshould not be read into or against the parent application or otherrelated applications.

FIELD

The present application relates to wireless communications, and moreparticularly DC offset cancelation in wireless receivers.

DESCRIPTION OF THE RELATED ART

Wireless communication systems are rapidly growing in usage.Additionally, there exist numerous different wireless communicationtechnologies and standards. Some examples of wireless communicationtechnologies include GSM, UMTS (associated with, for example, WCDMA orTD-SCDMA air interfaces), LTE, LTE Advanced (LTE-A), HSPA, 3GPP2CDMA2000 (e.g., 1×RTT, 1×EV-DO, HRPD, eHRPD), IEEE 802.11 (WLAN orWi-Fi), IEEE 802.16 (WiMAX), Bluetooth, and others.

Conventionally, frequency division multiplexing (FDM) systems such asOFDM avoid transmission of data on tones corresponding to basebanddirect current (DC) signals to avoid interference by the DC signals.Such interference may be caused by leakage of the local oscillator atthe receiver, for example. Analog cancelation of the DC interference maybe insufficient to reliably receive signals on carrier frequencies nearlocal oscillator frequencies. Refraining from transmitting usingsubcarriers corresponding to DC, however, may reduce bandwidth, whichmay be especially costly in the context of narrowband receivers.

SUMMARY

Techniques are disclosed relating to DC interference cancelation inreceived wireless signals. Disclosed techniques may be performed in thedigital domain, in conjunction with analog cancelation techniques. Insome embodiments, a receiver apparatus operates a local oscillator at afrequency corresponding to a particular pilot symbol in a receivedwireless signal. In some embodiments the receiver estimates DCinterference at the frequency based on the received pilot symbol (thismay be facilitated by the fact that the contents of pilot symbols areknown, because they are typically used for channel estimation). In someembodiments, the receiver apparatus is configured to cancel the DCinterference based on the estimate to determine received data insubsequently received signals at the frequency.

In some embodiments, the receiver is configured to cancel the DCinterference based on an analysis of multiple pilot symbols at thefrequency. This may increase cancelation performance but may reduceoverall bandwidth, relative to DC interference estimation based on asingle pilot symbol. Disclosed techniques may allow narrowband receiversto efficiently use more of their allocated frequency bandwidth, ratherthan wasting bandwidth near the frequency of the local oscillator.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present subject matter can be obtainedwhen the following detailed description of the embodiments is consideredin conjunction with the following drawings, in which:

FIG. 1 illustrates an exemplary (and simplified) wireless communicationsystem, according to some embodiments.

FIG. 2 illustrates a base station (BS) in communication with a userequipment (UE) device, according to some embodiments.

FIG. 3 illustrates an exemplary block diagram of a UE, according to someembodiments.

FIG. 4 illustrates exemplary bandwidth allocations, according to someembodiments.

FIG. 5 illustrates an exemplary oscillator frequency that is selected tocorrespond to a pilot subcarrier, according to some embodiments.

FIG. 6 illustrates an exemplary method for DC interference cancelation,according to some embodiments.

FIG. 7 illustrates an exemplary computer-readable medium, according tosome embodiments.

While the features described herein may be susceptible to variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and are herein described indetail. It should be understood, however, that the drawings and detaileddescription thereto are not intended to be limiting to the particularform disclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the subject matter as defined by the appended claims.

DETAILED DESCRIPTION

Acronyms

-   -   The following acronyms may be used in the present disclosure.    -   3GPP: Third Generation Partnership Project    -   3GPP2: Third Generation Partnership Project 2    -   APN: Access Point Name    -   BLER: Block Error Rate (same as Packet Error Rate)    -   BER: Bit Error Rate    -   CRC: Cyclic Redundancy Check    -   DL: Downlink    -   GBR: Guaranteed Bit Rate    -   GSM: Global System for Mobile Communications    -   IMS: IP Multimedia Subsystem    -   IP: Internet Protocol    -   LTE: Long Term Evolution    -   MME: Mobility Management Entity    -   MO: Message Originating    -   MT: Message Terminating    -   NAS: Non-access Stratum    -   PCC: Policy and Charging Control    -   PCEF: Policy and Charging Enforcement Function    -   PCRF: Policy and Charging Rules Function    -   PCSCF: Proxy Call Session Control Function    -   PGW: Packet Gateway    -   PER: Packet Error Rate    -   QCI: Quality of Service Class Index    -   QoS: Quality of Service    -   RRC: Radio Resource Control    -   SGW: Serving Gateway    -   SINR: Signal to Interference-and-Noise Ratio    -   SIR: Signal to Interference Ratio    -   SNR: Signal to Noise Ratio    -   Tx: Transmission    -   UE: User Equipment    -   UL: Uplink    -   UMTS: Universal Mobile Telecommunication System    -   VoLTE: Voice Over LTE        Terms

The following is a glossary of terms used in this disclosure:

Memory Medium—Any of various types of non-transitory memory devices orstorage devices. The term “memory medium” is intended to include aninstallation medium, e.g., a CD-ROM, floppy disks, or tape device; acomputer system memory or random access memory such as DRAM, DDR RAM,SRAM, EDO RAM, Rambus RAM, etc.; a non-volatile memory such as a Flash,magnetic media, e.g., a hard drive, or optical storage; registers, orother similar types of memory elements, etc. The memory medium mayinclude other types of non-transitory memory as well or combinationsthereof. In addition, the memory medium may be located in a firstcomputer system in which the programs are executed, or may be located ina second different computer system which connects to the first computersystem over a network, such as the Internet. In the latter instance, thesecond computer system may provide program instructions to the firstcomputer for execution. The term “memory medium” may include two or morememory mediums which may reside in different locations, e.g., indifferent computer systems that are connected over a network. The memorymedium may store program instructions (e.g., embodied as computerprograms) that may be executed by one or more processors.

Carrier Medium—a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and/or other physicaltransmission medium that conveys signals such as electrical,electromagnetic, or digital signals.

Computer System—any of various types of computing or processing systems,including a personal computer system (PC), mainframe computer system,workstation, network appliance, Internet appliance, personal digitalassistant (PDA), television system, grid computing system, or otherdevice or combinations of devices. In general, the term “computersystem” can be broadly defined to encompass any device (or combinationof devices) having at least one processor that executes instructionsfrom a memory medium.

User Equipment (UE) (or “UE Device”)—any of various types of computersystems devices which are mobile or portable and which performs wirelesscommunications. Examples of UE devices include mobile telephones orsmart phones (e.g., iPhone™, Android™-based phones), portable gamingdevices (e.g., Nintendo DS™ Play Station Portable™, Gameboy Advance™,iPhone™), laptops, wearable devices (e.g., a smart watch, smartglasses), PDAs, portable Internet devices, music players, data storagedevices, or other handheld devices, etc. In general, the term “UE” or“UE device” can be broadly defined to encompass any electronic,computing, and/or telecommunications device (or combination of devices)which is easily transported by a user and capable of wirelesscommunication.

Base Station—The term “Base Station” has the full breadth of itsordinary meaning, and at least includes a wireless communication stationinstalled at a fixed location and used to communicate as part of awireless cellular telephone system or cellular radio system.

Processing Element—refers to various elements or combinations ofelements that are capable of performing a function in a device, such asa user equipment or a cellular network device. Processing elements mayinclude, for example: processors and associated memory, portions orcircuits of individual processor cores, entire processor cores,processor arrays, circuits such as an ASIC (Application SpecificIntegrated Circuit), programmable hardware elements such as a fieldprogrammable gate array (FPGA), as well any of various combinations ofthe above.

Channel—a medium used to convey information from a sender (transmitter)to a receiver. It should be noted that since characteristics of the term“channel” may differ according to different wireless protocols, the term“channel” as used herein may be considered as being used in a mannerthat is consistent with the standard of the type of device withreference to which the term is used. In some standards, channel widthsmay be variable (e.g., depending on device capability, band conditions,etc.). For example, LTE may support scalable channel bandwidths from 1.4MHz to 20 MHz. In contrast, WLAN channels may be 22 MHz wide whileBluetooth channels may be 1 Mhz wide. Other protocols and standards mayinclude different definitions of channels. Furthermore, some standardsmay define and use multiple types of channels, e.g., different channelsfor uplink or downlink and/or different channels for different uses suchas data, control information, etc.

Band—The term “band” has the full breadth of its ordinary meaning, andat least includes a section of spectrum (e.g., radio frequency spectrum)in which channels are used or set aside for the same purpose.

Automatically—refers to an action or operation performed by a computersystem (e.g., software executed by the computer system) or device (e.g.,circuitry, programmable hardware elements, ASICs, etc.), without userinput directly specifying or performing the action or operation. Thusthe term “automatically” is in contrast to an operation being manuallyperformed or specified by the user, where the user provides input todirectly perform the operation. An automatic procedure may be initiatedby input provided by the user, but the subsequent actions that areperformed “automatically” are not specified by the user, i.e., are notperformed “manually,” where the user specifies each action to perform.For example, a user filling out an electronic form by selecting eachfield and providing input specifying information (e.g., by typinginformation, selecting check boxes, radio selections, etc.) is fillingout the form manually, even though the computer system must update theform in response to the user actions. The form may be automaticallyfilled out by the computer system where the computer system (e.g.,software executing on the computer system) analyzes the fields of theform and fills in the form without any user input specifying the answersto the fields. As indicated above, the user may invoke the automaticfilling of the form, but is not involved in the actual filling of theform (e.g., the user is not manually specifying answers to fields butrather they are being automatically completed). The presentspecification provides various examples of operations beingautomatically performed in response to actions the user has taken.

FIGS. 1 and 2—Communication System

FIG. 1 illustrates an exemplary (and simplified) wireless communicationsystem, according to some embodiments. It is noted that the system ofFIG. 1 is merely one example of a possible system, and embodiments maybe implemented in any of various systems, as desired.

As shown, the exemplary wireless communication system includes a basestation 102A which communicates over a transmission medium with one ormore user devices 106A, 106B, etc., through 106N. Each of the userdevices may be referred to herein as a “user equipment” (UE). Thus, theuser devices 106 are referred to as UEs or UE devices.

The base station 102A may be a base transceiver station (BTS) or cellsite, and may include hardware that enables wireless communication withthe UEs 106A-106N. The base station 102A may also be equipped tocommunicate with a network 100 (e.g., a core network of a cellularservice provider, a telecommunication network such as a public switchedtelephone network (PSTN), and/or the Internet, among variouspossibilities). Thus, the base station 102A may facilitate communicationbetween the user devices (UEs) and/or between the UEs and the network100.

The communication area (or coverage area) of the base station may bereferred to as a “cell.” The base station 102A and the UEs 106 may beconfigured to communicate over the transmission medium using any ofvarious radio access technologies (RATs), also referred to as wirelesscommunication technologies, or telecommunication standards, such as GSM,UMTS (WCDMA, TD-SCDMA), LTE, LTE-Advanced (LTE-A), HSPA, 3GPP2 CDMA2000(e.g., 1×RTT, 1×EV-DO, HRPD, eHRPD), Wi-Fi, WiMAX etc.

Base station 102A and other similar base stations (such as base stations102B . . . 102N) operating according to the same or a different cellularcommunication standard may thus be provided as a network of cells, whichmay provide continuous or nearly continuous overlapping service to UEs106A-160N and similar devices over a wide geographic area via one ormore cellular communication standards.

Thus, while base station 102A may act as a “serving cell” for UEs106A-160N as illustrated in FIG. 1, each UE 106 may also possibly comewithin communication range of, and be capable of receiving signals from,one or more other cells (which might be provided by base stations 102B-Nand/or any other base stations), which may be referred to as“neighboring cells.” Such cells may also be capable of facilitatingcommunication between user devices and/or between user devices and thenetwork 100, according to the same wireless communication technology asbase station 102A and/or any of various other possible wirelesscommunication technologies. Such cells may include “macro” cells,“micro” cells, “pico” cells, and/or cells which provide any of variousother granularities of service area size. For example, base stations102A-B illustrated in FIG. 1 might be macro cells, while base station102N might be a micro cell. Other configurations are also possible.

Note that a UE 106 may be capable of communicating using multiplewireless communication standards. For example, a UE 106 may beconfigured to communicate using a wireless networking (e.g., Wi-Fi)and/or peer-to-peer wireless communication protocol (e.g., BT, Wi-Fipeer-to-peer, etc.) in addition to at least one cellular communicationprotocol (e.g., GSM, UMTS (WCDMA, TD-SCDMA), LTE, LTE-A, HSPA, 3GPP2CDMA2000 (e.g., 1×RTT, 1×EV-DO, HRPD, eHRPD), etc.). The UE 106 may alsoor alternatively be configured to communicate using one or more globalnavigational satellite systems (GNSS, e.g., GPS or GLONASS), one or moremobile television broadcasting standards (e.g., ATSC-M/H or DVB-H),and/or any other wireless communication protocol, if desired. Othercombinations of wireless communication standards (including more thantwo wireless communication standards) are also possible.

FIG. 2 illustrates user equipment 106 (e.g., one of the devices106A-106N) in communication with a base station 102 (e.g., one of thebase stations 102A-102N), according to some embodiments. The UE 106 maybe a device with cellular communication capability such as a mobilephone, a hand-held device, a wearable device, a computer or a tablet, orvirtually any type of wireless device.

The UE 106 may include a processor that is configured to execute programinstructions stored in memory. The UE 106 may perform any of the methodembodiments described herein by executing such stored instructions.Alternatively, or in addition, the UE 106 may include a programmablehardware element such as an FPGA (field-programmable gate array) that isconfigured to perform any of the method embodiments described herein, orany portion of any of the method embodiments described herein.Alternatively, or in addition, the UE 106 may include one or moreintegrated circuits configured to perform any of the method embodimentsdescribed herein.

The UE 106 may include one or more antennas for communicating using oneor more wireless communication protocols or technologies. In someembodiments, the UE 106 is configured to communicate using either ofCDMA2000 (1×RTT/1×EV-DO/HRPD/eHRPD) or LTE using a single shared radioand/or GSM or LTE using the single shared radio. The shared radio maycouple to a single antenna, or may couple to multiple antennas (e.g.,for MIMO) for performing wireless communications. In general, a radiomay include any combination of a baseband processor, analog RF signalprocessing circuitry (e.g., including filters, mixers, oscillators,amplifiers, etc.), or digital processing circuitry (e.g., for digitalmodulation as well as other digital processing). Similarly, the radiomay implement one or more receive and transmit chains using theaforementioned hardware. For example, the UE 106 may share one or moreparts of a receive and/or transmit chain between multiple wirelesscommunication technologies, such as those discussed above.

In some embodiments, the UE 106 may include separate (and possiblymultiple) transmit and/or receive chains (e.g., including separate RFand/or digital radio components) for each wireless communicationprotocol with which it is configured to communicate. As a furtherpossibility, the UE 106 may include one or more radios which are sharedbetween multiple wireless communication protocols, and one or moreradios which are used exclusively by a single wireless communicationprotocol. For example, the UE 106 might include a shared radio forcommunicating using either of LTE or 1×RTT (or LTE or GSM), and separateradios for communicating using each of Wi-Fi and Bluetooth. Otherconfigurations are also possible.

FIG. 3—Exemplary Block Diagram of a UE

FIG. 3 illustrates an exemplary block diagram of a UE 106, according tosome embodiments. As shown, the UE 106 may include a system on chip(SOC) 300, which may include processing elements for various purposes.For example, as shown, the SOC 300 may include processor(s) 302 whichmay execute program instructions for the UE 106 and display circuitry304 which may perform graphics processing and provide display signals tothe display 360. The processor(s) 302 may also be coupled to memorymanagement unit (MMU) 340, which may be configured to receive addressesfrom the processor(s) 302 and translate those addresses to locations inmemory (e.g., memory 306, read only memory (ROM) 350, NAND flash memory310) and/or to other circuits or devices, such as the display circuitry304, wireless communication circuitry 330, connector I/F 320, and/ordisplay 360. The MMU 340 may be configured to perform memory protectionand page table translation or set up. In some embodiments, the MMU 340may be included as a portion of the processor(s) 302.

As shown, the SOC 300 may be coupled to various other circuits of the UE106. For example, the UE 106 may include various types of memory (e.g.,including NAND flash 310), a connector interface 320 (e.g., for couplingto a computer system, dock, charging station, etc.), the display 360,and wireless communication circuitry 330 (e.g., for LTE, Wi-Fi, GPS,etc.).

The UE device 106 may include at least one antenna (and possiblymultiple antennas, e.g., for MIMO and/or for implementing differentwireless communication technologies, among various possibilities), forperforming wireless communication with base stations and/or otherdevices. For example, the UE device 106 may use antenna(s) 335 toperform the wireless communication. As noted above, the UE 106 may beconfigured to communicate wirelessly using multiple wirelesscommunication technologies in some embodiments.

As described further subsequently herein, the UE 106 may includehardware and software components for implementing features and methodsdescribed herein. The processor 302 of the UE device 106 may beconfigured to implement part or all of the methods described herein,e.g., by executing program instructions stored on a memory medium (e.g.,a non-transitory computer-readable memory medium). In other embodiments,processor 302 may be configured as a programmable hardware element, suchas an FPGA (Field Programmable Gate Array), or as an ASIC (ApplicationSpecific Integrated Circuit). Alternatively (or in addition), theprocessor 302 of the UE device 106, in conjunction with one or more ofthe other components 300, 304, 306, 310, 320, 330, 335, 340, 350, 360may be configured to implement part or all of the features describedherein.

Although disclosed embodiments are discussed in the context of a mobiledevice, similar techniques may be used for non-mobile devices, such asbase stations, for example, in other embodiments.

Overview of DC Interference at Wireless Receivers

Wireless receivers typically down-convert incoming signals at differentcarrier frequencies to an intermediate frequency (IF) by mixing theincoming signals with signals generated by a local oscillator (LO). Inmany implementations (e.g., direct-conversion receivers where the localoscillator's frequency is the same as, or close to, the carrierfrequency of the intended signal) local oscillator energy may leakthrough the mixer stage. This may create a DC offset signal that mayinterfere with received signals.

Traditionally, the modulation of the DC tone is skipped in OFDM systemsto avoid this interference. This may reduce overall bandwidth, which maybe significant in narrowband receivers. Narrow-band receivers may oftenbe used in low-power devices, where efficient utilization of availablebandwidth is important to reduce battery drain, for example.

In the example shown in FIG. 4, the right-most rectangle represents aportion of the frequency band (centered at FRBs) that is assigned to aparticular receiver. The other two rectangles represent portions of thefrequency band allocated to other users. One design option would use alocal oscillator frequency for this receiver at F_(C), which would avoidDC offset for the received signals. This, however, would consumeadditional power because of the need for a higher bandwidth receiver forthe rest of the analog chain, including baseband filters, ADCs, etc. Incontrast, a narrowband receiver may be used if the local oscillator iscentered at F_(RBs), but this introduces the DC offset interference, asdiscussed above. Generally, narrowband receivers may consume lesserpower than wider-band receivers, e.g., because their ADCs can run at alower frequency. Also note that placing the local oscillator frequencybetween subcarriers may still result in DC interference to thosesubcarriers because of spillage.

Therefore, in some embodiments, wireless receiver circuitry (e.g., in UE106) is configured to estimate and cancel the DC offset in order todemodulate a corresponding tone. In some embodiments, DC offsetcancelation is performed in both the analog and digital domains. Theanalog cancelation may be performed using known calibration techniques,in some embodiments. In various embodiments, analog cancelation alonemay not entirely cancel the DC offset, leaving a residual DC offset inoutput signals from an analog to digital converter (ADC). At least aportion of this DC offset may be canceled in the digital domain, invarious embodiments, as discussed below.

Exemplary DC Cancelation Techniques

FIG. 5 illustrates received signaling that includes six resource blocks(RBs) at different frequencies allocated to the receiver, according tosome embodiments. In the illustrated embodiment, pilot symbols in thefirst, fourth, seventh, and tenth subcarrier in each RB are shown usingsolid circles for illustration. In some embodiments, the receiver isconfigured to place the local oscillator frequency at a subcarrierfrequency corresponding to a pilot symbol (at F_(rx) in the example ofFIG. 5). This may prevent the pilot symbol(s) at this subcarrier in thisRB from being used for channel estimation, but may facilitate DC offsetcancelation. In some embodiments, the wireless receiver circuitry isconfigured to select a subcarrier at or near the middle of its allocatedfrequency band (e.g., if the six resources blocks of FIG. 5 areallocated, F_(rx) is in the middle of this band). Note that F_(rx) isselected, in some embodiments, based on the frequency band assigned tothe receiver by a base station. Thus, the receiver may operate its localoscillator at different frequencies, in various embodiments, dependingon the allocated frequency band.

In some embodiments, the wireless receiver circuitry is configured toestimate the DC offset at the local oscillator frequency based on thepilot symbol. For example, equation (1) below describes a relationshipbetween received and transmitted signals, according to some embodiments:Y _(k) =H _(k) X _(k) +DC+N  (1)where Y_(k) represents a received signal, X_(k) represents a known pilotsymbol included in the received signal, H_(k) represents the channel, DCrepresents the DC offset, and N represents noise. The wireless receivercircuitry may determine the DC offset based on the received signal, theknown pilot symbol, and channel estimates that it determines based onother pilot symbols (e.g., using 2D interpolation in time andfrequency).

In some embodiments, the wireless receiver circuitry is configured togenerate a channel estimate corresponding to the pilot symbol usinginterpolation, e.g., in the time and/or frequency dimensions, based onchannel estimates for other nearby pilot symbols. Thus, the inability touse the particular pilot symbol for channel estimation may have littleto no effect on channel estimation performance.

In some embodiments, the wireless receiver circuitry is configured tocancel the estimated DC offset in order to demodulate data on thesubcarrier in subsequently received RBs at the oscillator frequency (notshown in FIG. 6). For example, the wireless receiver circuitry maysubtract the estimated DC offset from the signal being processed. Thismay allow use of the subcarrier for data reception even though itoverlaps with the local oscillator frequency. Note that any dataresource elements on the particular subcarrier in the RB with the pilotsymbol may be unused or lost, but this may typically correspond to onlya small portion of a communication. This may increase availablebandwidth for receivers by using the subcarrier corresponding to DC,without significantly reducing performance.

In some embodiments, placing the local oscillator at the center of asubcarrier may avoid spillage to adjacent subcarriers. In otherembodiments, DC offset spillage may also be estimated and canceled.Further, the disclosed techniques may be backwards compatible, as theymay be performed by a UE without knowledge of the base station or a needto alter wireless communications standards.

In some embodiments, the wireless receiver circuitry is configured togenerate a DC estimate by averaging over multiple pilot symbols, e.g.,using a filter in the time domain. A Kalman filter is one example ofsuch a filter, although other filter types may be used as appropriate.For example, the receiver may use multiple different pilot symbolsreceived at different times to generate DC estimates and filter the DCestimates to generate a filtered DC estimate. Any of various appropriatefilters, averages, and/or weights may be used to generate such a DCestimate. Depending on the number of pilot symbols used, this mayslightly reduce throughput (e.g., because data symbols on thesubcarriers used for DC estimation are lost) while increasing theperformance of the DC cancelation relative to DC estimates using asingle pilot symbol.

Exemplary Method

FIG. 6 is a flow diagram illustrating a method for DC interferencecancelation, according to some embodiments. The method shown in FIG. 6may be used in conjunction with any of the computer circuitry, systems,devices, elements, or components disclosed herein, among other devices.In various embodiments, some of the method elements shown may beperformed concurrently, in a different order than shown, or may beomitted. Additional method elements may also be performed as desired.Flow begins at 610.

At 610, in the illustrated embodiment, an apparatus operates a localoscillator for a wireless receiver at a frequency corresponding to apilot symbol in a received signal. The local oscillator may utilize aphase-locked loop (PLL) to achieve the desired frequency. Note that itis well understood that the local oscillator operating at the samefrequency as the subcarrier does not necessarily mean that thefrequencies are exactly identical (at least because it is highlyunlikely that any two real-world signals have exactly the samefrequency). Rather, setting the local oscillator to the subcarrierfrequency means that the subcarrier and local oscillator are at the samenominal frequency over a particular time interval, with variations fromthe nominal frequency within acceptable bounds.

At 620, in the illustrated embodiment, the apparatus does not use thepilot symbol for channel estimation, but uses interpolation to determinea channel estimate corresponding to the pilot symbol based on one ormore nearby pilot symbols. The nearby pilot symbols may be close to thepilot symbol in frequency and/or time. In some embodiments, thisinterpolation may be omitted and the pilot symbol may simply be ignored.

At 630, in the illustrated embodiment, the apparatus estimates DCinterference at the frequency based on the received pilot symbol. Insome embodiments, this estimation is based on equation (1), for example.

At 640, in the illustrated embodiment, the apparatus cancels the DCinterference based on the estimate to determine (e.g., demodulate)received data in subsequent received signals at the frequency. Note that“canceling” the DC interference may not entirely eliminate theinterference, e.g., based on errors in the estimate and/or imperfectionsin subtraction of the estimated DC offset. Rather, the term “canceling”is to be construed according to its well-understood meaning in the art,which includes reducing the magnitude of the signal being canceled(e.g., by subtracting the signal being canceled or applying the inverseof the signal being canceled), which may allow detection of otherdesired signals.

In some embodiments, the method elements of FIG. 6 are performed in thedigital domain, after conversion of received analog symbols to digitalsymbols. As discussed above, the techniques of FIG. 6 may be used inconjunction with analog cancelation of DC offset.

The disclosed techniques may allow a low power receiver to achievebetter performance for channel allocations smaller than the channelbandwidth (e.g., in LTE). In some embodiments, the entire receive chainis narrowband, such that information is only captured in the bandwidthassigned to the receiver. This may be particularly useful for low-powerdevices that are link-budget limited. The disclosed techniques mayminimize performance loss (e.g., for small allocations such as 1.4 MHzchannels, losing one subcarrier may be significant). Further, asdiscussed above, the receiver may place the local oscillator frequencyindependent of any control by the base station, providing backwardscompatibility with existing network infrastructure, in variousembodiments.

Exemplary Computer-Readable Medium

The present disclosure has described various exemplary circuits indetail above. It is intended that the present disclosure cover not onlyembodiments that include such circuitry, but also a computer-readablestorage medium that includes design information that specifies suchcircuitry. Accordingly, the present disclosure is intended to supportclaims that cover not only an apparatus that includes the disclosedcircuitry, but also a storage medium that specifies the circuitry in aformat that is recognized by a fabrication system configured to producehardware (e.g., an integrated circuit) that includes the disclosedcircuitry. Claims to such a storage medium are intended to cover, forexample, an entity that produces a circuit design, but does not itselffabricate the design.

FIG. 7 is a block diagram illustrating an exemplary non-transitorycomputer-readable storage medium that stores circuit design information,according to some embodiments. In the illustrated embodimentsemiconductor fabrication system 720 is configured to process the designinformation 715 stored on non-transitory computer-readable medium 710and fabricate integrated circuit 730 based on the design information715.

Non-transitory computer-readable medium 710, may comprise any of variousappropriate types of memory devices or storage devices. Medium 710 maybe an installation medium, e.g., a CD-ROM, floppy disks, or tape device;a computer system memory or random access memory such as DRAM, DDR RAM,SRAM, EDO RAM, Rambus RAM, etc.; a non-volatile memory such as a Flash,magnetic media, e.g., a hard drive, or optical storage; registers, orother similar types of memory elements, etc. Medium 710 may includeother types of non-transitory memory as well or combinations thereof.Medium 710 may include two or more memory mediums which may reside indifferent locations, e.g., in different computer systems that areconnected over a network.

Design information 715 may be specified using any of various appropriatecomputer languages, including hardware description languages such as,without limitation: VHDL, Verilog, SystemC, SystemVerilog, RHDL, M,MyHDL, etc. Design information 715 may be usable by semiconductorfabrication system 720 to fabrication at least a portion of integratedcircuit 730. The format of design information 715 may be recognized byat least one semiconductor fabrication system 720. In some embodiments,design information 715 may also include one or more cell libraries whichspecify the synthesis and/or layout of integrated circuit 730. In someembodiments, the design information is specified in whole or in part inthe form of a netlist that specifies cell library elements and theirconnectivity. Design information 715, taken alone, may or may notinclude sufficient information for fabrication of a correspondingintegrated circuit. For example, design information 715 may specify thecircuit elements to be fabricated but not their physical layout. In thiscase, design information 715 may need to be combined with layoutinformation to actually fabricate the specified circuitry.

Semiconductor fabrication system 720 may include any of variousappropriate elements configured to fabricate integrated circuits. Thismay include, for example, elements for depositing semiconductormaterials (e.g., on a wafer, which may include masking), removingmaterials, altering the shape of deposited materials, modifyingmaterials (e.g., by doping materials or modifying dielectric constantsusing ultraviolet processing), etc. Semiconductor fabrication system 720may also be configured to perform various testing of fabricated circuitsfor correct operation.

In various embodiments, integrated circuit 730 is configured to operateaccording to a circuit design specified by design information 715, whichmay include performing any of the functionality described herein. Forexample, integrated circuit 730 may include any of various elementsshown in FIGS. 1-3. Further, integrated circuit 730 may be configured toperform various functions described herein in conjunction with othercomponents. Further, the functionality described herein may be performedby multiple connected integrated circuits.

As used herein, a phrase of the form “design information that specifiesa design of a circuit configured to . . . ” does not imply that thecircuit in question must be fabricated in order for the element to bemet. Rather, this phrase indicates that the design information describesa circuit that, upon being fabricated, will be configured to perform theindicated actions or will include the specified components.

Embodiments of the present disclosure may be realized in any of variousforms. For example some embodiments may be realized as acomputer-implemented method, a computer-readable memory medium, or acomputer system. Other embodiments may be realized using one or morecustom-designed hardware devices such as ASICs. Still other embodimentsmay be realized using one or more programmable hardware elements such asFPGAs.

In some embodiments, a non-transitory computer-readable memory mediummay be configured so that it stores program instructions and/or data,where the program instructions, if executed by a computer system, causethe computer system to perform a method, e.g., any of a methodembodiments described herein, or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets.

Embodiments described as using a particular technology (e.g., customcircuitry) may also be implemented using other technologies (e.g., aprocessor and a memory, an FPGA, etc.).

In some embodiments, a device (e.g., a UE 106) may be configured toinclude a processor (or a set of processors) and a memory medium, wherethe memory medium stores program instructions, where the processor isconfigured to read and execute the program instructions from the memorymedium, where the program instructions are executable to implement anyof the various method embodiments described herein (or, any combinationof the method embodiments described herein, or, any subset of any of themethod embodiments described herein, or, any combination of suchsubsets). The device may be realized in any of various forms.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. An apparatus, comprising one or more processingelements configured to: operate a local oscillator at a frequencycorresponding to a particular pilot symbol in a received wirelesssignal, wherein the received wireless signal includes pilot symbols atmultiple different frequencies; estimate, based on the particular pilotsymbol, direct current (DC) interference at the frequency; and adjust,based on the estimated DC interference, one or more signals subsequentlyreceived at the frequency.
 2. The apparatus of claim 1, wherein theapparatus is configured to estimate the DC interference based on thereceived wireless signal, known data of the particular pilot symbol, andchannel conditions determined based on other pilot symbols.
 3. Theapparatus of claim 1, wherein the apparatus is configured not to use theparticular pilot symbol for channel estimation.
 4. The apparatus ofclaim 1, wherein the one or more processing elements are furtherconfigured to estimate a value for the particular pilot symbol usinginterpolation based on other pilot symbols.
 5. The apparatus of claim 1,wherein the one or more processing elements are further configured toestimate the DC interference based on multiple pilot symbols at thefrequency that are received at different times.
 6. The apparatus ofclaim 1, wherein the apparatus is a mobile device that further comprisesat least one antenna configured to receive the wireless signal and atleast one radio connected to the at least one antenna.
 7. The apparatusof claim 1, wherein to adjust the one or more signals, the apparatus isconfigured to subtract the estimated DC interference from the one ormore signals.
 8. The apparatus of claim 1, wherein to adjust the one ormore signals, the apparatus is configured to apply an inverse of theestimated DC interference to the one or more signals.
 9. The apparatusof claim 1, wherein the estimated DC interference is an estimate ofleakage of energy from the local oscillator.
 10. The apparatus of claim1, wherein the one or more processing elements are further configured toperform analog reduction of DC interference prior to adjustment of theone or more signals based on the estimated DC interference.
 11. Amethod, comprising: operating, by a computing device, a local oscillatorat a frequency corresponding to a particular pilot symbol in a receivedwireless signal, wherein the received wireless signal includes pilotsymbols at multiple different frequencies; estimating, by the computingdevice based on the particular pilot symbol, direct current (DC)interference at the frequency; and adjusting, by the computing devicebased on the estimated DC interference, one or more signals subsequentlyreceived at the frequency.
 12. The method of claim 11, wherein theestimating is based the received wireless signal, known data of theparticular pilot symbol, and channel conditions determined based onother pilot symbols.
 13. The method of claim 11, further comprisingomitting the particular pilot symbol from a channel estimationprocedure.
 14. The method of claim 11, wherein the adjusting includessubtracting the estimated DC interference from the one or more signals.15. The method of claim 11, wherein the estimated DC interference is anestimate of leakage of energy from the local oscillator.
 16. A mobiledevice, comprising: one or more antennas; one or more radios configuredto wirelessly communicate via the one or more antennas; and processorcircuitry configured to: operate a local oscillator at a frequencycorresponding to a particular pilot symbol in a received wirelesssignal, wherein the received wireless signal includes pilot symbols atmultiple different frequencies; estimate, based on the particular pilotsymbol, direct current (DC) interference at the frequency; and adjust,based on the estimated DC interference, one or more signals subsequentlyreceived at the frequency.
 17. The mobile device of claim 16, whereinthe estimate is based the received wireless signal, known data of theparticular pilot symbol, and channel conditions determined based onother pilot symbols.
 18. The mobile device of claim 16, wherein theadjustment includes subtracting the estimated DC interference from theone or more signals.
 19. The mobile device of claim 16, wherein theadjustment includes an application of an inverse of the estimated DCinterference to the one or more signals.
 20. The mobile device of claim16, wherein the processor circuitry is further configured to performanalog reduction of DC interference prior to adjustment of the one ormore signals based on the estimated DC interference.